Nanospot welder and method

ABSTRACT

A method and apparatus for assembly of small structures is disclosed. The present invention discloses electron beams created from one or more nanotips in an array operated in a field emission mode that can be controlled to apply heat to very well defined spots. The multiple electron beams may be generated and deflected and applied to electron beam heating and welding applications.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present invention claims priority to the following:

[0002] Provisional Patent Application Serial No. 60/469,381, entitled“CARBON NANOTUBE HIGH CURRENT DENSITY ELECTRON SOURCE,” filed on May 9,2003;

[0003] Provisional Patent Application Serial No. 60/508,815, entitled“NANOSPOT WELDER AND METHOD,” filed on Oct. 3, 2003; and

[0004] Provisional Patent Application Serial No. 60/549,200, entitled“NANOSPOT WELDER AND METHOD FIELD OF THE INVENTION,” filed on Mar. 2,2004.

TECHNICAL FIELD

[0005] The present invention relates in general to the creation of weldjoints in small structures.

BACKGROUND INFORMATION

[0006] 1. Electron Sources

[0007] Researchers have been working on developing electron sourcesusing carbon nanotubes (CNTs) for about ten years. One of the earliestreferences to this work is the patent of Keesmann et al. (U.S. Pat. No.5,773,921). Some examples of the applications of using CNT electronsources are for displays (field emission displays and cathode ray tubesare two examples), e-beam lithography, x-ray sources and microwavedevices (traveling wave tubes, klystrons, magnetrons, etc.). Some ofthese applications require high currents and high current densities, inthe range of 1-100 Amps/cm², in both pulsed and continuous wave (CW) ordirect current (DC) modes. Many of these applications requiring highcurrent densities are now being met using hot (thermal) cathodes ofvarious types. All of these hot cathodes require power to heat thecathode and maintain its temperature in the range of 1000° C.

[0008] Other cold cathode technologies exist, but many of these requirefabricating arrays of micron-size microtips. These are expensive tofabricate and not very reliable in extreme environments. This isevidenced by the fact that several companies that have made an effort tomake microtip-based field emission displays have recently abandonedtheir efforts. Trying to incorporate microtip cathodes into microwaveand x-ray devices has also met with limited success. On the other hand,carbon nanotube electron sources have been made with very inexpensiveprocesses (such as printing or dispensing) over large areas.

[0009] Gated microtip electron sources, despite their weaknesses, didhave an advantage of generating high current densities. (SRIInternational claimed 11.6 Amps/cm² at 250V, “Application of FieldEmitter Arrays to Microwave Power Amplifiers,” D. R. Whaley et al.,Abstracts of the International Vacuum Electronics Conf, May 2-4, 2000,Monterey, Calif.; NEC Corporation claimed 1.27 Amps/cm² from a Simicrotip gated device “Field-Emitter-Array Cathode-Ray-Tube (FEA-CRT),”K. Konuma et al., SID 99 Digest p. 1151, 1999; Extreme Devices claimed 4Amps/cm² using what they claim as “diamond cathode technology,” Specsheet for E-Chip ED138-250 dated March 2003—Rev. 2; see also “AMicromachined Vacuum Triode Using a Carbon Nanotube Cold Cathode,” C.Bower, et al., IEEE Trans on Electron Devices, Vol. 49, No. 8, p. 1478,August, 2002.)

[0010] The literature of carbon nanotube electron sources has examplesof achievement of a few Amps/cm². (E.g., claim of 4 Amp/cm² with totalcurrent of only 0.4 mA in “Large current density from carbon nanotubefield emitters,” W. Zhu et al., App. Phys. Let. Vol. 75, No. 6, p. 873,August, 1999.) Most of these claims were sources operated in a diodemode (ungated, anode and cathode only) and thus are of limited use forthe applications of interest. What is needed is a gated electron sourceusing carbon nanotube cathodes that can achieve high current densities.Some attempts have been made to make a gated source using carbonnanotubes (one example is D. S. Y. Hsu, et al., “Integrally Gated CarbonNanotube-on-Post Field Emitter Arrays”, App. Phys. Lett., Vol. 80.,p118, 2002). The best that has been achieved is on the order of 0.1Amps/cm².

[0011] There are a couple of reasons why gated, high current densityelectron sources have not been made. The CNT cathodes are not regulararrays of nanotubes that are positioned in an exact formation andaligned in an exact direction. Instead, they are irregularly positionedand randomly oriented. In some cases, the alignment is preferential in acertain direction; but, unless the position and the alignment of theCNTs are engineered precisely, it will be difficult to design andengineer an optimized gated structure such as is done for microtipsources. The lack of optimization leads to poor efficiency of theemitted electrons (many of them strike the gate structure, creating heatthat will ultimately lead to device destruction) and poor use of cathodearea (much of the area is dedicated to gate structure and not CNTemitters). Many of the carbon nanotubes are also not optimized for highcurrent electron emission. They can unravel or become hot anddisintegrate. Increasing the density of carbon nanotubes is not asolution either because they electrically screen each other from theapplied electric field needed to extract the electrons from thenanotubes (see Jean Marc Bonard et al. “Tuning the Field EmissionProperties of Patterned Carbon Nanotube Films,” Advanced Materials, 13,184 (2001)). Thus, there is a need to increase the means of increasingthe current density of gated electron emission devices using CNTcathodes.

[0012] One means of increasing the current density is to use an approachthat is similar to what van der Vaart et al. have described in U.S.Patent Application Publication US 2002/0053867 A1 (see alsoInternational Publication Number WO 00/79558 A1). This approach is alsodescribed in papers published in the SID literature (“Technology for theHopping Electron Cathode,” P. J. A. Derks, et al., SID 02 Digest, p.1396; “A Novel Cathode for the CRTs based on Hopping ElectronTransport,” N. C. van der Vaart,” SID 02 Digest, p. 1392; “A NovelElectron Source for CRTs,” van der Vaart et al., Information Display,Vol. 18, No. 6, p. 14, June 2002).

[0013] In this Hopping Electron Cathode (HEC) approach, the electronsfrom a thermal cathode are “condensed” by a funnel-shaped structure thatis coated with a layer of secondary electron emitter material. FIG. 1illustrates how this approach works. The electrons from a hot cathodeare extracted by use of a gauss electrode (grid) from the cathode andthen strike the funnel. Secondary electrons are generated when thevoltage of the electrode at the top of the funnel is sufficiently highenough (about 300-500V). Because the funnel surface is insulating andcharge conservation must be maintained, the current is neither amplifiednor degraded, but collected by the funnel to the opening at the end ofthe funnel. Using this approach, very high electron current densitiescan be emitted from the funnel opening, exceeding 1000 Amps/cm².

[0014] 2. Welding

[0015] With smaller and smaller structures and assemblies required formany applications, there is a need for assembly and welding technologiesfor the smaller structures. As just one example, there is a need forwelding fine hydrogen separation membranes into very small reactors(micro-reactors). There is also a need for heat treatment on a finescale and with high resolution. High throughput is also required forproduct manufacturing. There are several methods for welding two piecesof material together.

[0016] Contact welding (tack welding)—This involves forcing high currentin a short pulse though the two parts. Typically, the joint between thetwo parts is highly resistive compared to the bulk of the materials andthis area is heated rapidly by the pulse current. The temperature canrise to near or over the melting point of one or more of the materialsand a bond is created between the materials. Typically, the size scalefor this type of welding is on the order of 1 mm or larger. In thiscase, both parts must be metallic.

[0017] Wire bonding—Wire bonding is similar to contact welding.Ultra-sound can be applied in addition to high pulse current to create abond. The size scale is on the order of 0.1 mm and can be highlyautomated. This is good for making interconnects to integrated circuitsand printed circuit boards, but limited in making other assemblies.

[0018] Laser bonding—A laser can be focused to a small spot and createlocal heating to make a bond. Mirrors on micropositioners can direct thebeam to many different spots. This approach is flexible but it isdifficult to make a multibeam system to increase the throughput. Inaddition, metals reflect a large percentage of the light, decreasing theefficiency of the welder. The size of the spot is on the order of 0.1 mmto 0.01 mm.

[0019] Focused Ion Beam (FIB)—FIB systems are much like scanningelectron microscopes (SEMs). FIBs can focus a beam to nano-scale sizes;10 nanometer features have been demonstrated. This approach can achievethe fine resolution required for many applications, but FIB machines areexpensive systems and the throughput is very low because only one beamis available to do all the machining. FIB systems are typically used formicromachining by etching material away and are not used for welding.

[0020] Electron beam welders or Scanning Electron Microscopes(SEMs)—Electron beam welders use a electron gun to weld joints in avacuum environment. Typically, the focus of the electron beam is 0.1 mmto 1.0 mm. SEMs can focus to much finer resolutions, but typically havevery small currents, not sufficient for welding or bonding. Both systemsuse only one beam to perform all the processes. The size of the beam(welding spot) and the through put of standard electron beam welders andSEM machines are not sufficient for many nanospot welding and heattreatment applications. An e-beam welder is needed that can be sealed toan array for multibeam approaches and also achieve small beam sizes.

[0021] It is therefore a desire to provide a nanospot welder and methodthat addresses the need for assembly apparatus and methods for verysmall structures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The foregoing and other features and aspects of the presentinvention will be best understood with reference to the followingdetailed description of a specific embodiment of the invention, whenread in conjunction with the accompanying drawings, wherein:

[0023]FIG. 1 illustrates a prior art hopping electron cathode (HEC);

[0024]FIG. 2 illustrates a gated HEC;

[0025]FIG. 3 illustrates a graph of current versus hopping electronblades potential;

[0026]FIG. 4 illustrates anode and grid currents allotted as a functionof an extraction field;

[0027]FIG. 5 illustrates a HEC with electrostatic focusing elements;

[0028]FIG. 6 illustrates an image created by an electron beam using theembodiment illustrated in FIG. 5;

[0029]FIG. 7 illustrates an array of HEC sources;

[0030]FIG. 8 is a representative view of a nanospot welder;

[0031]FIG. 9 is an image of a CNT fiber on the end of an AFM tip;

[0032]FIG. 10 is a an image of a carbon nanotip on the end of a tungstenneedle;

[0033]FIG. 11 is a representative side view of a nanospot welder;

[0034]FIG. 12 is a representative view of another embodiment of ananospot welder utilizing a multiple electron beam;

[0035]FIG. 13 is a representative cross-sectional view of a gated CNTelectron source;

[0036]FIG. 14 is a representative view of another embodiment of thepresent invention;

[0037]FIG. 15 is an image of a result of using an embodiment of thepresent invention; and

[0038]FIG. 16 is an image of an array of HEC sources and a work pieceisolated in two separate chambers by the funnel array of the HEC source.

DETAILED DESCRIPTION

[0039] In the following description, numerous specific details are setforth such as specific display configurations, etc. to provide athorough understanding of the present invention. However, it will beobvious to those skilled in the art that the present invention may bepracticed without such specific details. In other instances, well-knowncircuits have been shown in block diagram form in order not to obscurethe present invention in unnecessary detail. For the most part, detailsconcerning timing considerations and the like have been omitted in asmuch as such details are not necessary to obtain a completeunderstanding of the present invention and are within the skills ofpersons of ordinary skill in the relevant art.

[0040] Referring to FIG. 2, the funnel is two blades of alumina 201 thatare shaped to form a slit funnel. A cylindrical funnel can also be used,such as described in the Philips papers.

[0041]FIG. 3 shows the efficiency of the HEC 204 vs. the blades 201potential. The prior art literature mentions the potential on the funnelelectrodes of nearly 500-700V is needed. However, it is seen that thepotential of 150-200V is good enough to force the electrons to come outfrom the slit 202. The efficiency of the source (the ratio of emittedcurrent from the cathode 204 to the current collected at the anode 203)increased from 0 to about 67% when the potential on the funnel electrodewas increased. The beam image on the phosphor screen 203 also changed:from a small single spot at low voltage to a two-lobe structure athigher voltage on the blades.

[0042] It should be noted that the current in the blade electrodes 201was much lower then the grid and anode currents. Furthermore, the anodecurrent can be modulated with the bias on the funnel electrode. Themodulation is linear with funnel potential from 0V to about 140V.Additional experiments showed that this modulation potential from 0 to100% swing is roughly independent of the current that is delivered fromthe cathode/grid assembly (e-gun). In other words, the graph shows thatthe 140V swing on the potential will modulate the current from theelectron gun from 0 to 2.2 mA. If the grid voltage on the electron gunwas increased, then the electron gun would be capable of emitting highercurrents (the grid current at 0V on the funnel electrode would behigher) and the anode current with 140V on the funnel electrode wouldalso be proportionally higher.

[0043] In FIG. 3, at zero potential on the funnel electrode, the entirecathode current goes to the extraction grid. As the funnel electrodepotential (HEC blade potential) increases, more of the emitted currentis condensed and passes through the funnel 202 and is then collected bythe anode 203. Efficiency is the ratio of the anode current to the totalcurrent emitted from the cathode 204 and is plotted as a fraction100%=1.0 in the graph.

[0044] The graph in FIG. 4 measures the I-V curve at constant voltage onthe funnel electrode. The objective of this task is to obtain a peakanode current of ˜25 mA in a pulse mode. The pulse width was 10 μs,frequency 100 Hz, ballast resistor of 25 kOhm in series with thephosphor anode. The potential on the funnel electrodes was held at 500Vconstant and the extraction grid voltage in the electron gun 204 wasramped up.

[0045] In FIG. 4, the anode 203 and grid currents are plotted as afunction of the extraction field generated between the cathode and thegrid 204. The funnel electrode 201 potentials were held constant at500V. Efficiency is also plotted as the percentage of total emittedcurrent from the cathode collected at the anode. A value of 35 on theplot corresponds to 70% efficiency.

[0046] This shows that the current through the funnel 202 and collectedat the anode 203 is about 30 mA. Since the gap 202 in the funnel is only0.005 cm×0.4 cm, then the current density of electrodes flowing throughthe gap is about 15 Amps/cm². The current along the length of the slit202 is not uniform, the current in the center is much higher because theelectron gun source is round and not rectangular. Thus the currentdensity in the center of the slit 202 is probably 30 Amps/cm² or higher.

[0047] A method of overcoming the inherent current density limitationsof gated electron sources is performed using carbon nanotube emitters bycondensing the beam from a CNT gated electron source into a narrowerbeam of electrons. Current densities as high as 15 Amps/cm² weredemonstrated. By making the funnel a cylindrical funnel and not theslit, it is expected that current densities as high as 1000 Amp/cm² canbe achieved. This current can be modulated with voltages between 0 and150V; the current modulation is linear in proportion to the potential onthe funnel electrode. This was demonstrated by operating a test circuitas shown in FIG. 2 in a pulsed mode (duty factor of 0.1%). Similarperformance is expected with operating in a CW or DC mode.

[0048] The beam coming from the funnel can be accelerated, focused withelectrostatic or magnetic focusing elements or deflected usingelectrostatic or magnetic deflection elements similar to what is used instandard CRT electron guns. FIG. 5 shows how the electrostatic focusinglens 507, 508 can be used to focus the electrons coming through thefunnel.

[0049]FIG. 6 shows an image on anode 503 where the beam can indeed befocused to a narrow beam using the focusing elements 507, 508.

[0050] Referring to FIG. 7, it is also possible to make an integratedarray of funnels for pixilated electron sources. This array can be x-yaddressable. This can be done in a couple of ways. The electron sourcesbefore the funnel can be x-y addressed or a control line that also actsas the funnel electrode can be patterned on the exit side of the funnelarray. The funnel array can be made out of alumina, glass or otherinsulator. It can be coated with MgO in the funnel openings to improvethe secondary electron performance of the funnel. The funnel exit holescan be circular, rectangular or other shapes. The funnel array can thenbe placed on a patterned electron source (a CNT source is illustrated,but the source can be microtips, a thermal cathode, or other sources),the pattern of the electron source aligning with the openings (largeend) of the funnel. Each funnel in the array condenses the electronsthat enter it from the large opening. An unpatterned electron source mayalso be used if a flood of electrons is needed It is also possible tomake just a linear array of sources, similar to what is shown in FIG. 7,but aligned only in one row. Each of these sources can be independentlycontrolled in intensity. The focus and deflection of the each of thesources can be together (in tandem) or separately. The openings of thesources can be as small as 0.5 microns for fine-focus x-ray sources ormultibeam e-beam lithography applications. Display applications can havemuch larger dimensions. The hopping electron cathode or funnel approachalso has the advantage in that the work piece and the electron sourcecan be isolated from each other by the funnel array. The holes of thefunnel can be made very small (as small as 0.5 micron as noted earlier)so the opening area through the funnel array to the electron sources canbe a very small percentage of the total array area. Gasses created inthe work area where the electrons hit the work piece can be blocked fromentering the area of the electron sources, increasing the stability andlife of the electron sources. FIG. 16 shows the work piece in a separatechamber from the electron sources, separated by the funnel array. (Thefunnel array can have as few as one funnel in principle.) Differentvacuum or gas environments can be placed in each of the chambers. Forexample, a strong vacuum pump (not shown in FIG. 16) can be used toevacuate the electron source chamber to a better vacuum than the workpiece chamber (e.g. 10⁻⁷ Torr in electron source chamber and 10⁻³ Torrin work piece chamber). Different gas environments can also be used toin the work piece chamber than in the electron source chamber. Forexample, a high partial pressure of Ar gas can be used in the work piecechamber and a high partial pressure of H₂ gas can be used in theelectron source chamber. Other gasses and arrangements are alsopossible. The small openings of the funnel will allow some gases to mixbetween the chambers but this will be limited by the size of theopenings and to a smaller degree by the shape of the funnel. Smallfunnel openings and long, narrow funnels will limit the gas mixingbetween the two chambers.

[0051] The work piece is show in FIG. 16 without any support. In fact,supports will be needed to control the gap (z direction) between thefunnel and the work piece and also to allow the work piece to movelaterally with respect to the funnel (x and y, y is out of the paper).These supports are not shown to simplify the figure; these supports arewell known in the state of the art.

[0052]FIG. 8 is a representative view of a nanospot welder in accordancewith an embodiment of the present invention. The nanospot welderincludes a modified Atomic Force Microscope (AFM) or a ScanningTunneling Microscope (STM) machine to make a beam of electrons that areaccelerated at high energy in a beam to heat a small spot. Atomic ForceMicroscopes and Scanning Tunneling Microscopes are also described underthe term Scanning Probe Microscopes (SPM). The AFM or STM tip is not incontact with the work piece during the welding process. The tip isoperated in a field emission (FE) mode such that electrons are extractedfrom the tip. The electrons are accelerated to the work piece to locallyheat and bond material. The tip may remain stationary during the bondingprocess or it can be scanning. Before the bonding process, the tip maybe used in a AFM or STM mode to locate the bond site accurately. Whenthe bond site is located, the tip may be withdrawn to a distance andoperated in a field emission mode.

[0053] The expected operating mode of this device would be to place thewelder tip a small distance away from the sample. These gap distancesare on the order of 10 nm to as large as 100 microns, depending on thespot size of the beam required and how much voltage one would like toput on the welder tip. Since the device operates in a diode mode (nogate structure), the beam current, welder tip voltage and gap arevariables that are interdependent. If the gap is 100 microns, then 1000Vcould be placed on the welder tip to draw about 2 micro-Amps of currentfrom the tip to the work piece. This creates a beam power of 2 mWattsand a local power density of 100 Watts/cm2 for a spot size expected tobe about 50 microns in diameter. These numbers are estimates and serveonly as a description of the expected mode of operation. Smaller gapsmay lead to lower voltage on the needle, but in turn may lead to smallerspot size. Even though the total power in the beam may decrease, thepower density may not change nearly as much.

[0054] The tip can be coated with a carbon film to increase durability.The tip may be a carbon-based microtip. Tips made of alloys or compoundsof carbon are also good for this application. A carbon nanotube fibercan be grown from the tip end of the microtip as described in (U.S. Pat.No. 5,773,921). An image of a CNT fiber grown on the end of an AFM tipis shown in U.S. Pat. No. 6,146,227 and included as FIG. 9.

[0055] It is also possible to fabricate a smaller tip on the end of alarger tip or needle. In the publication by S. D. Johnson et al.(“Carbon Nanotips for Field-Emission Electron Guns” Abstracts of the 47^(th) International Conference on Electron, Ion and Photon BeamTechnology and Nanofabrication, Tampa, Fla., May 27-May 30, 2003, p274),a carbon nanotip is grown on the end of a tungsten needle. This is shownin FIG. 10.

[0056] Referring to FIG. 11, the nanospot welder may include one tip ora gang of tips on a single or multiple boards. The gang of tips can bein an array on a printed circuit board. Each tip can be independentlyaddressable in both gap (displacement) and/or voltage on the tip. Eitherone will regulate the current emitted from the tip. Driver chips mountedon the PCB can drive each tip individually or two or more in tandem. ThePCB is displaced from the work piece by a small gap that is controlledby supports and actuators on the work piece and PCB (not shown). The PCBand/or the work piece can be moved relative to each other in order toallow the tips to address the full area of the work piece. Current isdrawn from each of the tips by increasing the voltage to the tip of bychanging the gap of the tip to the work piece. The gap between the workpiece and each of the tips may be individually controlled.

[0057]FIG. 12 is a representative view of another embodiment of thenanospot welder of the present invention. This embodiment of thenanospot welder includes a multiple electron beam. In this embodiment,several electron beams are used to provide heat treatment or to performwelding tasks. Typically, the beams would be in an array. The currentand voltage of each beam may be independently controlled although thetypical mode of operation would be to keep the beam voltage the same foreach and modulate the current of each beam as a function of time andposition of the beam on the work piece.

[0058] The beam current can be modulated by a control or extraction gridover the cathode. The cathode can be thermal (hot cathode) or cold(microtips or carbon nanotubes or photocathodes). The beam currents canalso be pulse-width modulated to control the duty factor of the beam ONtime. The electron source may be a hopping electron cathode using eithera thermal electron source or a cold electron source (including carbonnanotubes) to achieve electron source current densities as high as 15Amps/cm² or higher. The position of each beam can be controlled byelectrostatic deflection. An example of such a structure for a displayapplication is shown in FIG. 13, which also shows electrostatic focusingof the electron beam. A similar approach was taken for a display devicewas recently disclosed in “Flat CRT Display” and is incorporated intothis disclosure by reference to U.S. Pat. No. 6,411,020 andPCT/US99/01841-WO 99/39361. The beam focus can be controlled by therelative potential applied to focus electron and aperture electrodesrelative to the cathode and extraction grids.

[0059] The beams can also be controlled (deflected and focused) usingmagnetic fields. This is not shown, but similar methods are used tocontrol the electron beams in cathode ray tubes (CRTs) used as TVs,scanning electron microscopes and multiple-beam and projection e-beamlithography approaches (e.g., DiVa approach of Timothy Groves: T. R.Groves and R. A. Kendall; Journal of Vacuum Science and Technology,B16(6), Nov. 1998, p. 3168). Using a magnetic field parallel to thedirected electron beams as in the DiVa approach allows one to focus thebeams to very small spots (sub-micron) at periodic distances away fromthe source without using electrostatic lenses, making the systemfabrication much more simple. The magnetic fields can be generated usingstandard electromagnets in a Helmholz coil configuration as described inmost elementary physics texts. It is also possible in the embodiments tomove the work piece during the welding process. The movement can becontinuous or stop-and-go, depending on the application.

[0060] Yet another approach to making a nanospot welder is to use anelectron gun with a concentrator of electrons utilizing a mechanism ofelectrons hopping over the surface of a funnel-shaped or tapered holemade in a dielectric, where the electron drift toward the hole outlet ismaintained by applying an electric field oriented along the axis of thehole. Prior art of such an electron gun design includes, for example,Patent Applications US 2002/0053867, WO 00/79558, and WO 01/26131.

[0061] Referring to FIG. 14, the electric field is induced by applying apotential to a welded part that becomes an accelerating electrode and atarget at the same time. The energy of electrons is determined by thepotential on the target. It is possible to bring the target temperatureto a melting point or adjust the target temperature either by changingthe electron beam current, target potential, or use pulse-width or pulsefrequency modulation. More specifically, it is possible to bring thetarget temperature to a specified value by making a certain number ofelectron beam pulses.

[0062] Since the electrons diverge as they exit the hole, it isnecessary either to place the welded part close to the hole outlet oruse focusing electrodes. FIG. 14 depicts a concept where no focusingelectrodes are used, and spacers are used to ensure that melted metaldoes not interfere with the dielectric concentrator. The concentratormay have the hole of any geometrical shape, e.g., cone, square pyramid,or rectangular pyramid.

[0063] A part of the welder is an electron gun. The electron gun is asource of electrons, and it may be a gated source. It may be either athermionic cathode or cold cathode that uses field emission ofelectrons. In the described embodiment, a gated carbon nanotube coldcathode was used, which was capable of reaching up to 1 Amp/cm² ofelectron current. With such an electron gun and a rectangular shapedhole in a ceramic electron concentrator, the effect of melting a metalfoil was achieved where the welding spot has a diameter of nearly 50microns. FIG. 15 shows the photograph of the foil with a spot of meltedand then solidified metal.

[0064] The spot size that can be achieved depends on the design of thenanospot welder parts that, in turn, specifies an electron opticsconfiguration. Also, the spot size can be changed by varying the holeexit size. It is possible to make the size of the hole outlet ofsub-micron dimensions. As in previous two concepts, it is possible tomove the work piece during welding in a certain manner, eitherstop-and-go or continuously.

[0065] This concept can take a multiple-beam approach as well. A weldingarray can utilize either one electron gun with a mosaic concentrator,where the electron beam will split over multiple concentrators, or amultiple gun-concentrator system. A mosaic concentrator for a single-gundesign can be made of a single piece of dielectric, or a mosaic whereseams between parts are made in such a way that they do not result insignificant loss (or leak) of electron current. A multiple gun design isused where the beam configuration often needs to be changed, and/or thesystem is used for sub-millimeter (or larger scale), rather thensub-micron, welding.

[0066] From the foregoing detailed description of specific embodimentsof the invention, it should be apparent that a nanospot welder andmethod that is novel has been disclosed. Although specific embodimentsof the invention have been disclosed herein in some detail, this hasbeen done solely for the purposes of describing various features andaspects of the invention, and is not intended to be limiting withrespect to the scope of the invention. It is contemplated that varioussubstitutions, alterations, and/or modifications, including but notlimited to those implementation variations which may have been suggestedherein, may be made to the disclosed embodiments without departing fromthe spirit and scope of the invention as defined by the appended claimswhich follow.

What is claimed is:
 1. An apparatus comprising: an electron beam sourcepositioned a distance from a work piece to be welded; and a power supplyfor causing a beam of electrons to emit from the electron beam sourcetowards the work piece causing local heating at a desired spot on thework piece to thereby create a weld joint on the work piece.
 2. Theapparatus as recited in claim 1, wherein the electron beam source is ascanning probe microscope.
 3. The apparatus as recited in claim 1,wherein the electron beam source is an AFM microtip probe.
 4. Theapparatus as recited in claim 1, wherein the electron beam source is aSTM microtip probe.
 5. The apparatus as recited in claim 1, wherein theelectron beam source is a hopping electron cathode.
 6. An apparatuscomprising: a printed circuit board supporting a plurality of electronbeam sources; and circuitry for activating the plurality of electronbeam sources to each emit an electron beam to create a plurality of weldjoints on a work piece positioned a distance from the printed circuitboard.
 7. The apparatus as recited in claim 6, wherein the electron beamsource is a scanning probe microscope.
 8. The apparatus as recited inclaim 6, wherein the electron beam source is an AFM microtip probe. 9.The apparatus as recited in claim 6, wherein the electron beam source isa STM microtip probe.
 10. The apparatus as recited in claim 6, whereinthe electron beam source is a hopping electron cathode.
 11. Theapparatus as recited in claim 6, wherein the work piece is movablerelative to the printed circuit board.
 12. The apparatus as recited inclaim 6, wherein the plurality of electron beam sources are activated inparallel.
 13. The apparatus as recited in claim 6, wherein the pluralityof electron beam sources are arranged in an array on the printed circuitboard.
 14. A method for creating a weld joint comprising the steps ofpositioning an electron beam source a distance from a work piece; andactivating the electron beam source to emit an electron beam to a spoton the work piece to create the weld joint at the spot on the workpiece.
 15. The apparatus as recited in claim 14, wherein the electronbeam source is a scanning probe microscope.
 16. The apparatus as recitedin claim 14, wherein the electron beam source is an AFM microtip probe.17. The apparatus as recited in claim 14, wherein the electron beamsource is a STM microtip probe.
 18. The apparatus as recited in claim14, wherein the electron beam source is a hopping electron cathode. 19.An apparatus as recited in claim 18, wherein the electron source isseparated from the work piece by the HEC funnel array and additionalchamber walls.